The objective of the proposed research is to measure local rheological properties of the vascular interface and the underlying tissue and correlate these measurements with the histological structure of the underlying tissue in control animals and in animals with experimental atherosclerosis. The motivation for this study comes from the findings of recent researches which point to the possibility that the susceptibility of the various locations of the vascular surface to the atherosclerotic damage is strongly correlated with exposure to hydrodynamic shear stress and also to the local rheological properties of the arterial tissue. Among the specific properties being studied are the shear strength of the endothelial layer and the indentation resistance of the vascular intima and its supporting structures. The former involves the use of fine saline jets to erode the endothelium and the latter is carried out using a specially developed microindentor to apply small loads, the resulting indentation being measured by a linear transformer. BIBLIOGRAPHIC REFERENCES: "Mechanical Properties of Arteries," by D. J. Patel and R. N. Vaishnav, Ch. 12, Cardiovascular Flow Dynamics and Measurements, edited by Ned H. Hwang and Nils A. Normann, University Park Press, Baltimore, 1977, pp. 439-472. "Nonlinear Anisotropic Viscoelastic Properties of Canine Arterial Segments," by John T. Young, R. N. Vaishnav, and D. J. Patel, J. of Biomechanics, 1977 (in Press).